1. Field of the Invention
The invention set out and claimed here relates to providing electrical conductors for signal transmission between two mechanical structures, at least one of which is vibrating with respect to the other. The electrical conductors can be insulated with respect to each other and are arranged between the vibrating structures so that vibration does not cause fatigue and breaking of the conductors and also minimizes coupling of mechanical forces and damping between the structures.
2. Description of the Prior Art
The arrangements for mounting wires for transmission of electrical signals between vibrating structures which are continuously vibrated are in part limited by several consequences arising from the vibration. Prolonged alternating motion of wires can cause the wires to experience fatigue which leads to their breaking, or can lead to their kinking which in combination with the cyclic motion exacerbates fatigue and causes the wires to break.
Another consequence of mounting wires from vibrating structures is that damping forces or driving forces can be coupled to the vibrating structures. Damping forces arise for example from (1) friction between wires or in some arrangements friction between the wires and adjacent structures (these frictional forces arise even when the insulating material on the wires is a synthetic resin polymer lubricating material such as is sold under the trademark Teflon), and (2) the internal structure of the material itself. Examples of driving forces include those which result from adjacent vibrating machinery. Coupling damping and driving forces to vibrating structures will alter the motion of the vibrating structures, which in many applications is an unacceptable consequence when unaltered vibrating motion of the structure is to be measured.
As an example of an attempt to compromise these problems, it has been known in the manufacture of Coriolis mass flow rate meters where flow tubes are continuously vibrated with respect to support structures that wires can be wrapped around the flow tubes from their base, where the flow tubes are solidly mounted to a support and not vibrated, up to locations on the vibrated flow tubes where the wires are connected to sensors and other electrical components. Wires can also be laid along the length of flow tubes and taped or glued to them.
Having wires wrapped or affixed, by tape or glue for example, to vibrating structures substantially precludes kinking problems because the wires are essentially kept in line and prevented from kinking by the structure to which they are mounted. As for the problem of fatigue, if the mechanical characteristics of the wires are at least equivalent to or even better than those of the vibrated structure, mechanical fatigue of the wires is a comparable engineering problem to that for the vibrated structure. However, these solutions, wrapping, taping or gluing, add additional mass to the flow tubes due to either the additional lengths in the conductors when wound around the flow tubes or the added tape and glue. This additional mass can alter the vibrating motion of the structure. In addition, because the effects of humidity and temperature on the glue and tape are not uniform, differential damping in the glue and tape can occur which can alter the vibrating motion of the structures. Thus, it would be advantageous to have an apparatus for electrically interconnecting vibrating structures that would provide for secure attachment of the conductors while minimizing the conductor length or the use of tape and glue.
Addressing the problem of minimizing the coupling of damping and driving forces to vibrating structures is a distinct problem from preventing kinking and fatigue. Continuing with the example of Coriolis mass flow rate meters, unless the wires are very light, such as 34 gauge and the structure about which it is wrapped is substantially more massive, such as a 2.54 centimeter (cm) diameter stainless steel flow tube having a 0.3 cm wall thickness, the magnitude of coupled forces to the vibrating structure cannot necessarily be ignored. Another factor which can exacerbate the problem of forces being coupled to vibrating structures arises when wires are wrapped or in some way attached to more than one portion of a vibrating structure because the damping forces or driving forces coupled to the two portions may not be the same. Therefore, the sum of the different forces can cause the structure to twist.
Reducing the gauge of the wire used, tailoring the insulation on wires to minimize stiffness and friction, and using the most flexible but still temperature insensitive wire possible are -readily available considerations engineers can make when faced with the problem of transmission of electrical signals along conductors mounted between vibrating structures. However, these specification considerations alone will not always be sufficient. Accordingly, it is one object of the invention to provide a means for mounting wires between vibrating structures that will essentially minimize wire breakage and the coupling of damping and driving forces that can alter the motion of the vibrating structures. Another object of the invention is to be able to provide for secure attachment of the conductors to a vibrating structure while minimizing the conductor length or the use of tape and glue.